The combination of horizontal drilling and hydraulic fracturing has led to a rapid expansion of oil and gas exploration and development of unconventional reserves such as organic-rich shales. Concern about potential impacts on groundwater resources has stimulated research on new approaches for monitoring aquifers and for early detection of brine that may migrate into aquifers from shale gas development. Monitoring programs will rely on multiple tools to identify presence and concentrations of brine migration into aquifers. Moreover, multiple salinity sources commonly overlap in regions of unconventional gas development, necessitating reliable tools for source discrimination in a contamination event. The capability of naturally occurring, chemical tracers to provide insight into the fate and transport of injected and native fluids during extraction of oil and gas from unconventional reservoirs have gained interest from industry and regulatory agencies. The rare earth elements (REE; Sc, Y, and the lanthanides) are attractive for such applications owing to their consistent and predictable reactivities; fluids originating from various strata may be distinguishable on the basis of the dissolved REE concentrations and their inter-element relationships. In this talk we will report on our efforts in developing the REE as naturally-occurring, geochemical fingerprints of salinity sources. This includes an understanding of global REE abundance in groundwaters gained by statistical analyses of previously published data, total REE analysis of core and outcrop samples of the Marcellus shale, and the development of an efficient liquid-liquid extraction technique for determination of REE in small volumes of hyper-saline brines.

Exploring the potential for rare earth elements as geochemical fingerprints of salinity sources

249th National Meeting (2015)

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